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International Journal of Research in

Original Research Paper Narcosis in Hyperbaric Chamber Nurses

1,2 Denise F. Blake, 3Derelle A. Young and 4Lawrence H. Brown

1Emergency Department, The Townsville Hospital, Douglas, Queensland, Australia 2School of Marine and Tropical Biology, James Cook University, Townsville, Queensland, 4814, Australia 3Hyperbaric Medicine Unit, The Townsville Hospital, Townsville, Queensland, Australia 4Mount Isa Centre for Rural and Remote Health, Faculty of Medicine, Health and Molecular Sciences, James Cook University, Townsville, QLD, 4814, Australia

Article history Abstract: has become a specialty requiring high skill Received: 24-09-2014 and knowledge. is a perceived risk for all inside Revised: 03-10-2014 hyperbaric chamber nurses. The actual degree of impairment at Accepted: 16-12-2015 has not been quantified. Twenty eight subjects participated in the study.

Sixteen hyperbaric nurse candidates and five experienced hyperbaric Corresponding Author: Denise F. Blake, nurses completed Trail Making Test A (TMTA) pre and post compression Emergency Department, and at 180 kPa and 300 kPa. Seven experienced hyperbaric staff acted as The Townsville Hospital, an unpressurized reference. Time to completion of the test was recorded in Douglas, Queensland, Australia seconds; pre-test and perceived symptoms of narcosis at 300 kPa Email: [email protected] were also recorded. There were no statistically significant differences in the corrected TMT A times at the four different time periods. There was a trend to poorer performance by the nurse candidates at 180 kPa however this was not statistically significant. Most subjects felt some degree of narcosis at 300 kPa. Most hyperbaric chamber nurses can overcome the effects of nitrogen narcosis at 180 and 300 kPa to maintain or improve performance in the TMT A. Poor performance by hyperbaric nurse candidates maybe due to individual susceptibility or lack of ability to compensate. Due to the risk of nitrogen narcosis outside chamber staff should continue to make clinical decisions about patient care.

Keywords: Nitrogen Narcosis, Hyperbaric Research, Psychology, Nursing

Introduction to . The inside nurse attendant breathes air during either treatment other than during the final stages of Hyperbaric nursing is a specialty involved in the care when they breathe oxygen. It follows that of patients receiving hyperbaric oxygen treatment. there is a widely perceived risk of nitrogen narcosis for Nurses, from a wide background of experience including the inside nurse. Consequently the outside staff make all emergency and critical care, complete training in the patient care decisions and the inside nurse performs hyperbaric and . Hyperbaric nursing the skills at the request of the outside staff. However, the courses include both theoretical knowledge and practical actual degree of impairment in inside nurses has not been skills to equip nurses for working in the hyperbaric quantified. While much research has been done on environment. The nurses must be medically fit to “dive” SCUBA divers, mostly in (Biersner et al ., and perform training dives during their courses including 1978; Whitaker and Findley, 1977) in water and in dry a compression to 300 kilopascals (kPa). chambers, (Petri, 2003; Gallway et al ., 1991) no studies SCUBA divers with are treated have investigated the effect of nitrogen narcosis on in hyperbaric chambers using standardized treatment hyperbaric chamber nurses. tables. Two initial treatment tables are commonly used at Nitrogen narcosis was made famous in the Self The Townsville Hospital Unit. The Contained Underwater Apparatus (SCUBA) Royal Navy 62 (RN 62) treatment table prescribes diving community by who called it compression to 180 kPa and breathes oxygen. “l’ivresse des grandes profondeurs” or rapture of the The Comex 30 treatment table prescribes compression to great depths. Cousteau and Dumas (1958) It was 300 kPa and the diver breathes (50% and correctly associated with the effects of nitrogen 50% oxygen) until 180 kPa where they are changed over breathed under pressure by Behnke et al . (1935), but its

© 2014 Denise F. Blake, Derelle A. Young and Lawrence H. Brown. This open access article is distributed under a Creative Commons Attribution (CC-BY) 3.0 license.

Denise F. Blake et al . / International Journal of Research in Nursing 2014, 5 (2): 44.51 DOI: 10.3844/ijrnsp.2014.44.51 precise mechanism of action still remains controversial. time to complete TMT A and an increased number of Experimental evidence supports the importance of errors. As no formal assessment of susceptibility to in divers but variations in alveolar CO2 nitrogen narcosis is performed during hyperbaric tensions seems to have little effect on the magnitude of nursing courses, the aim of this study was to quantify the nitrogen component in narcosis. the effects of nitrogen narcosis on both experienced and Bennett and Rostain (2003). The traditional view was that novice hyperbaric chamber nurses during a nitrogen was an inert gas, highly soluble in and not compression to 180 and 300 kPa. involved in biochemical processes. However, more recent work has found that nitrogen acts on nerve cell membranes Methods interfering with impulse conduction (production, release and uptake of several neurotransmitters) most likely at the Participants synapses (Rostain et al ., 2011). Ethical approval was obtained from the Townsville The signs and symptoms of nitrogen narcosis have Health Service District Human Research Ethics been described as similar to those of alcohol Committee. (HREC/09/QTHS/2) Twenty eight subjects intoxication: Stimulation, excitement, and participated in the study. Relevant demographic data slowing of mental activity with delayed response to including alcohol consumption, body mass index, scuba stimuli. Early investigations demonstrated that at a depth diving experience and age were gathered from the of 30 metres of water (msw) (300 kPa) there is subjects’ diving medical examination record. The impairment of memory, , calculations, intervention group consisted of sixteen hyperbaric powers of association and fine motor functions and also nursing candidates and five experienced hyperbaric a tendency to fixate on ideas. Behnke et al . (1935) nurses. This group was pressurized to 300 kPa as a routine Intellectual functions are generally more severely affected part of the hyperbaric nursing course. The non-pressurized than manual dexterity. Increased concentration can reference group consisted of seven experienced hyperbaric ameliorate these effects. The effects of nitrogen narcosis staff currently working in the hyperbaric medicine unit. are variable, with some divers being more susceptible than All participants who were pressurized had a others. It may be potentiated by emotional instability, Australian Standard 4774.2 2002 dive medical. Written alcohol use, fatigue, hard work, apprehension and anxiety. informed consent was obtained. Frequent exposure to compressed air may afford some adaptation (Bennett and Rostain, 2003). Materials Various subjective feeling scales, physiological measurements and cognitive function tests have been The hyperbaric chamber used was the triple lock used to assess for nitrogen narcosis. Subjective feeling rectangular unit located at The Townsville Hospital, scales have attempted to equate the feelings of nitrogen Townsville, Queensland. The pressurizations were narcosis with that of (Monteiro et al ., undertaken in the inner lock, which has a working 1996; Hobbs, 2008) or delineate the effects of anxiety or pressure of 500 kPa and is used when completing an RN other emotional factors on the onset of nitrogen narcosis. 62 or Comex 30 treatment table. A certified hyperbaric Biersner et al . (1978); Gallway et al ., 1991; Davis et al ., technician operated the chamber for all pressurizations. 1972; Rogers and Moeller, 1989; Hamilton et al ., 1995) The TMT A was used as an objective measurement Studies using physiological measurements have of mental impairment during the pressurization. TMT A included heart rate and blood pressure (Biersner, 1987), is easy to perform, requires no objects that cannot be compressed and does not require an extensive amount of balance (Rogers and Moeller, 1989), EEG changes time to complete. Thus using TMT A does not influence (Pastena et al ., 2005) and critical flicker fusion the bottom time of the practice dive and does not require frequency. Balestra et al . (2012) Many different cognitive adjustment to the decompression schedule. TMT A was tests have been used in the research of nitrogen narcosis and initially developed as a test in the (AITB, 1944) and was no clear ideal test for quantifying nitrogen narcosis has yet incorporated into the Halstead-Reitan battery group of been identified. The cognitive function tests that have been tests in 1958. This test has been used to assess the used to measure nitrogen narcosis can be categorized into general intellectual ability of USA Army recruits (AITB, four behavioural endpoints: Reaction time, mental 1944) and to detect cognitive ability in aging drivers arithmetic, memory and manual dexterity. The specific test (Stutts et al ., 1998), dementia in the elderly (Reitan, chosen in each study appears dependent on the facility, 1958), portal systemic encephalopathy (Conn, 1977) and accessibility to equipment and the type of subjects. inert gas narcosis. Jakovljevic et al . (2012) It assesses This study was designed to determine whether visual scanning, number sequencing and visuomotor nitrogen narcosis occurs in hyperbaric chamber nurses speed. NBN (1997) The test is designed so that healthy during compression to 180 and 300 kPa using Trail individuals should be able to complete the test in less Making Test A (TMT A). It was expected that mild than 30 sec. However age and education level have been impairment would be seen at 300 kPa with increased found to influence results and normative data stratified

45 Denise F. Blake et al . / International Journal of Research in Nursing 2014, 5 (2): 44.51 DOI: 10.3844/ijrnsp.2014.44.51 by these variables have been developed and suggested as several training skills unrelated to the study. Subjects providing better reference values for impaired breathed 100% oxygen throughout the decompression performance (Tombaugh, 2004) and improving the from 140 kPa to 0 kPa as required during a normal reliability. NBN (1997) TMT A consists of 25 decompression from a Comex 30 or RN 62 treatment sequentially numbered circles distributed on a sheet of table. TMT A version 4 (T4) was completed on arrival paper, which the candidate must link with a pen in back at 0 kPa prior to exiting the chamber. The hyperbaric correct order whilst their performance is timed. The time technician responsible for compressing the chamber taken in seconds constitutes the ‘score’ for the test. ensured the dive was within the table limits. A hyperbaric There are four variations of the TMT A available and physician was in attendance during the compressions. they have been found to have the same degree of The reference group performed an identical sequence difficulty (Conn, 1977). of tests at similar inter-test time intervals whilst seated Hyperbaric staff outside the chamber acted as time inside the chamber, but without pressurization. There was keepers for each test (one time keeper per always a minimum of two staff in the reference group subject).Participants were asked to rate their level of testing sessions to approximate the testing environment. anxiety about the 300 kPa chamber dive during their first (baseline) TMT A assessment; after their last Data Analysis assessment participants were asked whether they felt like they experienced nitrogen narcosis at 300kPa and All data were entered into a Microsoft Excel 2003 if yes to describe the feeling as nitrogen narcosis is also (Microsoft Corporation, Redmond, Washington, USA) known to be expressed in a subjective component spread sheet and then exported into SPS Version 19 (Hamilton et al ., 1995). (IBM Company, Armonk, New York, USA) for Typically, the TMT is performed under direct analysis. Fisher’s exact Test (FET), Analysis of observation with errors in the number tracing sequence Variance (ANOVA) and Kruskal-Wallis (K-W) test identified and corrected immediately. This was not were used as appropriate to compare baseline possible in this study as the timers were outside of the demographic variables of the study groups. hyperbaric chamber. To adjust for this, the TMT forms For the primary analysis, each subject served as their own control. We determined change in TMT A time were reviewed following completion; where participants from baseline to each pressurization, as well as change in missed a number in their sequence tracing, a time TMT A time between each pressurization. We also penalty of 2 sec was added to their score for each error. determined the number of subjects who “failed” The two sec is an estimate of the time required for (corrected TMT A time >30 sec) at each protocol stage. redirection of the subject by the timer if an error had Although TMT A times were normally distributed been noted during the testing. across all study groups and all time points, changes in Design TMT A times were not universally normally distributed. Thus, we used Wilcoxon Sign Rank test to evaluate Prior to entering the chamber a ten number practice changes in TMT A time between each protocol stage. We test was completed to ensure that the subjects understood also used FET to evaluate associations between subjective the instructions and could perform the test. The feelings of narcosis and “failing” TMT A. A p-value less hyperbaric nurse candidates were then divided into than 0.05 was used to establish statistical significance. approximately equal sized groups (three or four) to perform the pressurizations. Each group had an Results experienced hyperbaric nurse as the inside attendant. The subjects then entered the chamber and were comfortably Hyperbaric nurse candidates were significantly seated. Prior to compression the subjects graded their younger than staff, but otherwise there were no significant differences in demographics between the subjective experience of anxiety about the 300 kPa pressurized group and the reference group. (Table 1) exposure (none, mild, moderate or severe). Test There were fewer males than females in the pressurized instructions were then read (and were re-read prior to group which is representative of the gender distribution each of the four tests). A different ‘parallel form’ of the in the nursing profession. test (in which the numbers are arranged differently) was Most (71%) of the experimental group subjects stated utilized for each of the four test repetitions performed by that they felt some level of narcosis at 300 kPa. One each subject. TMT A version 1 (T1) was completed at 0 subject, nurse candidate 2, had the feeling of being “very kPa and the pressurization subsequently commenced at a drunk” at 300 kPa, but had reported no anxiety prior to rate of 30 kPa per min. TMT A version 2 (T2) was the pressurization and performed the worst at 180 kPa. completed on arriving at 180 kPa. TMT A version3 (T3) (Table 2) Another nurse candidate, who had no anxiety was completed on arriving at 300 kPa and before the pressurization, stated they felt “happy and decompression was commenced after completion of embarrassed” at 300 kPa.

46 Denise F. Blake et al . / International Journal of Research in Nursing 2014, 5 (2): 44.51 DOI: 10.3844/ijrnsp.2014.44.51

Table 1: Baseline Demographics Nursing Reference Candidates Nursing Staff Group Significance N 16 5 7 Male [n, (%)] 4(25) 2(40) 4(57) FET, p = 0.368 Age (mean ± SD) 34(7) 44(4) 39(9) ANOVA, p = 0.038 SCUBA experience [n, (%)] 6(37.5) 1(20) 4(57) FET, p = 0.444 BMI (mean ± SD) 26.8(4.2) 26.8(4.2) 25.9(4.4) ANOVA, p = 0.875 Drinks/Week (median [IQR]) 2 [1-4] 10 [3-11] 4 [2-6] K-W, p = 0.143 Anxiety [n, (%)] 10(62.5) 1(20) N/A FET, p = 0.355 Symptoms of Narcosis [n, (%)] 12(75) 3(75) N/A FET, p = 0.648

Table 2. Raw results Trail Making Test a completion time in seconds; number of errors; corrected time T1 Time 1 T2 Time 2 T3 Time 3 T4 Time 4 Type T1 Errors Corrected T2 Errors Corrected T3 Errors Corrected T4 Errors Corrected Candidate* 1 24 0 24 19 0 19 17 0 17 13 0 13 Candidate 2 21 0 21 45 0 45 22 0 22 14 0 14 Candidate 3 22 0 22 34 1 36 24 0 24 22 0 22 Candidate 4 17 0 17 21 0 21 22 0 22 27 0 27 Candidate 5 33 0 33 26 0 26 21 0 21 23 0 23 Candidate 6 16 0 16 26 0 26 24 0 24 14 0 14 Candidate 7 37 0 37 33 0 33 22 0 22 28 0 28 Candidate 8 24 0 24 15 0 15 14 0 14 16 0 16 Candidate 9 16 0 16 18 0 18 14 0 14 15 0 15 Candidate 10 25 0 25 25 1 27 15 0 15 30 0 30 Candidate 11 21 0 21 26 0 26 18 0 18 28 0 28 Candidate 12 19 0 19 14 0 14 14 2 18 13 1 15 Candidate 13 25 2 29 23 2 27 18 1 20 21 0 21 Candidate 14 19 0 19 23 0 23 19 0 19 23 0 23 Candidate 15 14 0 14 19 0 19 21 0 21 27 1 29 Candidate 16 17 0 17 21 0 21 27 0 27 16 0 16 Experienced† 1 24 0 24 26 0 26 29 0 29 28 0 28 Experienced 2 22 0 22 21 0 21 22 0 22 27 0 27 Experienced 3 17 0 17 11 0 11 12 0 12 11 0 11 Experienced 4 20 0 20 21 0 21 18 0 18 22 0 22 Experienced 5 21 0 21 16 0 16 16 0 16 17 0 17 Reference¥ 1 17 0 17 31 0 31 20 0 20 24 0 24 Reference 2 16 0 16 18 0 18 14 0 14 13 0 13 Reference 3 28 0 28 21 0 21 25 0 25 31 0 31 Reference 4 14 0 14 12 0 12 16 0 16 15 0 15 Reference 5 16 0 16 14 0 14 15 0 15 15 0 15 Reference 6 24 0 24 17 0 17 15 0 15 23 0 23 Reference 7 17 0 17 14 0 14 16 0 16 16 0 16 *Hyperbaric Nursing Candidate, †Experienced Hyperbaric Nurse, ¥ Non-compressed Hyperbaric Staff

Table 2 shows the raw results. Two nurse candidates reference group, including the 95% confidence intervals exceeded 30 sec at T1; a third nurse candidate made two for the corrected TMT A completion times. errors at T1, but applying the 2-sec per error penalty still did Table 4 shows the median and inter quartile range not put this subject over the 30-sec threshold. Four subjects change in TMT A times at each protocol stage. From exceeded 30 sec at T2 (180 kPa), including three nurse baseline to T2 (180 kPa) there was not a statistically candidates (one of whom exceeded 30 sec at T1) and one significant change in completion time. There was a reference subject; three nurse candidates committed errors decrease in TMT A from T1 (180 kPa) to T3 (300 kpa). at T2; again applying the penalty for errors did not put any While this difference between T1 and T3 TMT A subject over the 30-sec threshold. All of the subjects times was not statistically significant, the decrease completed the TMT A in less than 30 sec at T3 (300 kPa), even after applying the penalty for two subjects who between T2 and T3 was significant. Finally, there was committed errors. At T4 one of the reference subjects no difference between the TMT A times recorded exceeded 30 sec. One nurse candidate accidentally after return to sea level and those recorded at any of swapped test one and four but got the same time of 22 sec the other protocol stages. on both tests so they were included in the analysis. Table 3 Table 4 also shows the results of subgroup shows the mean corrected TMT A times for the two analyses for nursing candidates and experienced staff, experimental subgroups and the reference group; Fig. 1 as well as those subjects who reported subjective graphically compares the corrected TMT A times for the feelings of narcosis. These results mirror those of the two subgroups of the experimental cohort and the overall analysis.

47 Denise F. Blake et al . / International Journal of Research in Nursing 2014, 5 (2): 44.51 DOI: 10.3844/ijrnsp.2014.44.51

Fig. 1. Mean and 95% confidence intervals of Trail Making Test A times for each group at each time point

Table 3. Mean (+SD) Corrected TMT A completion times, seconds Test 1 Test 2 Test 3 Test 4 Candidates* 22.1±6.4 24.8±8.1 19.9±3.7 20.9±6.2 Experienced† 20.8±2.6 19.0±5.7 19.4±6.5 21.0±7.1 Reference¥ 18.9±5.1 18.1±6.4 17.3±3.9 19.6±6.6 *Hyperbaric Nursing Candidate, †Experienced Hyperbaric Nurse, ¥Non-compressed Hyperbaric Staff

Table 4. Median (interquartile range) change in TMT A between , (seconds ) Change in Pressure Experimental Group T2-T1 T3-T1 T3-T2 T4-T3 T4-T1 Reference¥ (n=7) -2 (-7 to +2) -1 (-3 to +2) +1 (-4 to +4) 0 (-1 to +6) -1 (-1 to +3) p = 0.394 p = 0.395 p = 0.932 p = 0.223 p = 0.863 All Compressed (n=21) +2 (-5 to +4.5) -2 (-8 to +3.5) -2 (-7.5 to +1) +1 (-2.5 to +5) -1 (-1 to +4.5) p = 0.701 p = 0.197 p = 0.030 p = 0.338 p = 0.466 w/ Subjective Narcosis (n=15) +2 (-5 to +4) -2 (-10 to +2) -3 (-11 to +1) +2 (-4 to +5) -1 (-8 to +4) p = 0.569 p = 0.207 p = 0.018 p = 0.629 p = 0.245 Candidates* Only (n=16) +3 (-4.8 to +5) -1.5 (-9.8 to +4.3) -4 (-10.3 to +0.5) +1.5 (-3.8 to +5.8) -1.5 (-8 to +4.8) p = 0.392 p = 0.244 p = 0.018 p = 0.587 p = 0.410 Experienced† Only (n=5) -1 (-5.5 to +1.5) -2 (-5 to +2.5) +1 (-1.5 to +2) +1 (-1 to +4.5) +2 (-5 to +4.5) p = 0.416 p = 0.450 p = 0.577 p = 0.336 p =1.00 *Hyperbaric Nursing Candidates, †Experienced Hyperbaric Nurses, ¥Non-compressed Hyperbaric Staff

There was no association between subjective feelings Discussion of narcosis and the results of the TMT A at T2, FET p = 1.0 Nitrogen narcosis is a condition caused by breathing (Table 5) and no subjects exceeded the expected compressed air characterized by euphoria or anxiety and completion time of TMT A at T3. impairment of performance and reasoning. The conventional view taught on diving courses is that Table 5. Association between subjective narcosis and nitrogen narcosis can become apparent to divers breathing exceeding expected TMT A completion time air at depths of 30 msw (300 kPa). However, some Subjective Narcosis? researchers have suggested that impairment from nitrogen narcosis can be seen at shallower depths. Petri (2003); TMT A Result Yes No Davis et al ., 1972; Synodinos, 1976; Fowler, 1972) Mild Failed 3 0 signs and symptoms of nitrogen narcosis can be seen Not Failed 12 4 from 100 to 300 kPa with more severe manifestations of FET p = 1.00; sensitivity = 0.20; negative predictive value = 0.25 , unconsciousness and death at depths

48 Denise F. Blake et al . / International Journal of Research in Nursing 2014, 5 (2): 44.51 DOI: 10.3844/ijrnsp.2014.44.51 greater than 900 kPa. Lippmann and Mitchell, (2006) that those subjects who felt less intoxicated after The Comex 30 treatment table is used in Australia, but drinking also felt less nitrogen narcosis during a more commonly in the UK. (Sharpe, 2008) This simulated dive to 500 kPa (Monteiro et al ., 1996) and requires the inside chamber nurse to breathe air at 300 those more affected by alcohol were affected to a greater kPa, raising the possibility that they might be impaired degree by narcosis. Hobbs (2008) However, a link by nitrogen narcosis. between drinking history and nitrogen narcosis This study found that while most hyperbaric nurses susceptibility has not been established and this have subjective feelings of nitrogen narcosis they can phenomenon is probably related to individual overcome these effects at 180 kPa and 300 kPa to susceptibility. Hobbs (2008) The three hyperbaric nurse maintain (or in some cases improve) their timed candidates who did exhibit obvious decrements in performance in the TMT A. While we did not find any performance at 180 kPa declared minimal weekly alcohol statistically significant degradation in TMT performance, ingestion. This individual variation in susceptibility to three hyperbaric nurse candidates did exhibit obvious nitrogen narcosis may place some staff and patients, at decrements in performance at 180 kPa, possibly risk and perhaps assessment of hyperbaric inside nurse indicating an effect of nitrogen narcosis (Table 2). These candidates using the TMT A at 180 and 300kPa could apparent cognitive decrements in inexperienced subjects identify those more susceptible to nitrogen narcosis. could be interpreted as validating concerns about the potential for errors by attendant staff breathing air at Limitations common treatment pressures. However, it is notable that two of these subjects subsequently performed better at The lack of a convincing demonstration of nitrogen 300 kPa, when nitrogen narcosis would be expected to narcosis with a clear dose-response at the incrementally worsen. This result is difficult to interpret, but it raises greater ambient pressures was somewhat surprising the possibility that the initial decrement at 180 kPa may although consistent with a recent study. Jakovljevic et al . be related to factors other than narcosis. The distraction (2012) However, our study has several weaknesses that of ‘becoming accustomed to’ the initial deep may have distorted the result. First, TMT A is a blunt compression may have impaired performance. There was instrument and may not have been sensitive enough to also great competition between the participants, find a difference. Strauss et al . (2006) Two previous represented by friendly banter, as they heard the pens studies have used the Trail Making Tests to assess drawing lines on other participant’s pages perhaps nitrogen narcosis. Gallway et al . (1991) used a battery of leading to performance pressure on the candidates. The tests including TMT A and B. Gallway et al . (1991) candidates may not have thought that they should be They found no evidence of nitrogen narcosis and “narked” at 180 kPa and therefore may not have planned on repeating the testing with a longer period at concentrated as hard on the test at that time point. pressure prior to implementing the tests. A recent study The focus of most research on nitrogen narcosis has attempting to assess impairment during mild nitrogen been in the scuba diver (Hobbs, 2008; Davis et al ., 1972; narcosis with sub anaesthetic levels of used Balestra et al ., 2012; Synodinos, 1976) and not a computerized visual simple reaction time as well as hyperbaric nursing staff. Attempts have been made to TMT A and B. Jakovljevic et al . (2012) They did not find a significant impairment in performance stating that not only measure the effects of nitrogen narcosis but there is individual variation to the dose required to also to develop methods of adaptation especially for the induce nitrogen narcosis. professional diver. This has met with little success A test interrogating a wider range of cognitive (Petri, 2003; Rogers and Moeller, 1989; Biersner, 1987), domains may have been more sensitive such as TMT B however some studies suggest that subjects may be able to where the subject has to draw a line from the number 1 compensate for the effects of nitrogen narcosis. Petri (2003) to letter A up to number 12 and letter L in an alternating Our results support this finding as we did not find any fashion. However, one study using TMTs to assess statistical difference between hyperbaric nurse hepatic encephalopathy found that TMT A was candidates and experienced hyperbaric nurse sufficiently sensitive to detect changes and easier and performance. However, the three hyperbaric nurse faster to perform than TMT B. Conn (1977) Practice candidates who did exhibit decrements were not scuba effect may also become an issue using TMT B since as divers and therefore inexperienced with narcosis of yet there does not appear to be access to four different perhaps suggesting naivety to the ability to compensate. variations of the test. Practice effect could account for There is an assumption that nitrogen narcosis is the improvement at 300 kPa but there was no significant comparable to intoxication with alcohol, leading to the difference between test 1 and 4 for all groups so practice term “Martini’s Law”, where the effects of nitrogen did not seem to be a major factor. narcosis are likened to drinking one martini for each 10 The subjects were unblinded and motivated to msw. Studies looking at this relationship between perform well. The pressurization to 300 kPa was part of alcohol intoxication and nitrogen narcosis have found the hyperbaric nursing course and therefore all subjects

49 Denise F. Blake et al . / International Journal of Research in Nursing 2014, 5 (2): 44.51 DOI: 10.3844/ijrnsp.2014.44.51 were aware of the possibility of narcosis. There was a should remain outside the chamber with the outside reduction in TMT A times from T2 to T3 lending nurse attendant and all decisions about patient care evidence to the hypothesis that perhaps the nurses should be made by surface support staff not under the compensated for any effects of nitrogen narcosis by influence of increased partial pressures of nitrogen. concentrating harder on the task at 300 kPa. It has long Further research is needed to identify and validate the been long been thought that nitrogen narcosis occurs on best cognitive and motor tests for assessing nitrogen arrival to depth (Pastena et al ., 2005; Synodinos, 1976; narcosis in hyperbaric chamber nurse attendants. Fowler et al ., 1983) so our testing was performed within five minutes of arriving at 300 kPa. A recent study found Funding Information that, using critical flicker fusion frequency, impairment was worse after 15 min at 323 kPa than upon initial The authors have no support or funding to report. arrival at pressure. Balestra et al . (2012) Perhaps our results would be different if the nurse candidates Author’s Contributions performed their training skills first and then completed the TMT A prior to depressurization. All authors equally contributed in this study. Even though TMT A has been used to study nitrogen narcosis in the past it has not been validated Ethics for his purpose and the clinically significant change in This article is original and contains unpublished TMT A completion time has not been previously material. The corresponding author confirms that all of determined. Our study was adequately powered to the other authors have read and approved the manuscript detect a five second change in TMT A times. We found a mean increase of approximately 2.7 sec in TMT A and no ethical issues involved. time from baseline to 180 kPa among our primary study group. For a three second difference in TMT A to References achieve statistical significance would have required a AITB, 1944. Manual of directions and scoring. sample size of 27 subjects. Whether a three second or Washington, DC: War Department, Adjutant five second change in TMT A time is clinically General’s Office. significant, remains to be determined. Future plans would be to increase the numbers of Balestra, C., P. Lafère and P. Germonpré, 2012. participants in the study by performing the TMT A with Persistence of critical flicker fusion frequency each successive nursing course and/or changing to TMT impairment after a 33 mfw SCUBA dive: Evidence B which may be a more sensitive test to detect subtle of prolonged nitrogen narcosis? Eur. J. Appl. impairment by nitrogen narcosis. NBN (1997) Nurses Physiol., 112: 4063-4068. could also be assessed during routine 18:60:30 DOI: 10.1007/s00421-012-2391-z treatments or during RN 62 and Comex 30 treatments. A Behnke, A.R., R.M. Thomson and E.P. Motley, 1935. The performance test designed to replicate a nursing task, psychologic effects from breathing air at 4 atmospheres such as medication calculation or ventilator changes, pressure. Am. J. Physiol., 112: 554-558. would better assess and identify any clinically significant Bennett, P.B. and J.C. Rostain, 2003. Bennett and susceptibility to nitrogen narcosis at pressure. Also Elliott’s Physiology and Medicine of Diving. 5th replicating the study and blinding the nurses to the Edn., Saunders Ltd, ISBN-10: 0702025712, pp: 800. pressure level and performing the test prior to depressurization may show different results. Biersner, R.J., 1987. Emotional and physiological effects of nitrous oxide and hyperbaric air narcosis. Aviat Conclusion Space Environ. Med., 58: 34-38. PMID: 3814030 Biersner, R.J., D.A. Hall, P.G. Linaweaver and T.S. There was no statistically significant difference in the Neuman, 1978. Diving experience and emotional time taken to complete TMT A at 180 and 300 kPa. factors related to the psychomotor effects of Since most of the subjects stated that they felt some nitrogen narcosis. Aviat. Space Environ. Med., 49: degree of narcosis, this suggests that TMT A may not be 959-62. PMID: 678246 sensitive enough to detect mild levels of narcosis, Conn, H.O., 1977. Trailmaking and number-connection (Strauss et al ., 2006) and the current practice of not allowing the inside nurse attendant to make any major tests in the assessment of mental state in portal decisions while at 180 and 300kPa should not change. systemic encephalopathy. Digest Dis., 22: 541-550. The inside chamber nurse attendant should also be made DOI: 10.1007/BF01072510 aware that narcosis maybe present at 180 kPa, an issue Cousteau, J.Y. and F. Dumas, 1958. The Silent World. not previously emphasized. The hyperbaric physician 1st Edn., pp: 32.

50 Denise F. Blake et al . / International Journal of Research in Nursing 2014, 5 (2): 44.51 DOI: 10.3844/ijrnsp.2014.44.51

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